This may include rewriting sections to ensure they are clear and concise, and wikifying.

Reason: Several sections are likely outdated with the release of Mists of Pandaria and Warlords of Draenor.

The item level is a rather important property of every item. It has two main functions — reflect the item's usefulness and at the same time determine the minimum level a character must have in order to use it (see Minimum level requirements and Item Level section below). Also, item level is tied to many enchants which can only be applied to items of a particular item level or higher (usually 35, 60, or 300).

Up until Patch 3.2, the true item level was hidden in the game, and only UI mods can read it via the function GetItemInfo. Now, however, a new option has been added under Display in the Interface Options to show the item level on item tooltips.

As Hyzenthlei (Tauren Shaman 60 on Zul'Jin) first found out, and was later confirmed by a presentation at Blizzcon, Blizzard uses a formula to calculate item level from the item's stats.[citation needed] The following is an attempt to reverse-engineer this formula. This text is based on a forum post by Hyzenthlei (the original author) in the Blizzard forums, but that post has since disappeared.

During the original reverse-engineering of the individual "cost" of each stat, Hyzenthelei set out assuming that +1 to Heal had a cost of 100. He then compared items of similar item level and comparable stats and thus arrived at the first version of the StatMod table (which stood the test of time very well). Later, during a presentation by Blizzard at BlizzCon, a slide revealed that 1% Melee Crit = 14 points. This confirmed Hyzentheleis table (1% melee crit was indeed 14 times as expensive as one point of a basic stat), but at the same time gave a benchmark for the proper scale — rate basic stats with one point.

With WoW 2.0, the table was reworked, some properties (most notable Stamina) changed their price, and others were replaced. In particular many combat-related stats were changed to combat ratings. All existing items were updated to reflect this change. This simplified the table, because Combat Rating points are worth exactly one "item point", the same as base stats (exc. Stamina).

This may include rewriting sections to ensure they are clear and concise, and wikifying.

-- The following examples are all pre-wotlk formulas, which appear to have changed in 3.0.

The item level calculation was reverse-engineered upon a number of observations on the items in game:

Different statistics appear to be worth different amounts: One randomly enchanted item could have 40 attack power, 20 strength, or 30 stamina.

Different gear slots appear to be given different stat allocations: A helm or chestpiece has many more stats than gloves or a belt.

The more stats on an item, the more possible stats you may have. An item might have 50 Strength, or 35 Strength and 35 Spirit, or 28 each of 3 stats...

From these observations we are able to calculate the item level:
The calculation process.

The item is assigned its stats. Each stat has a different value denoted by its StatMod, listed in the table below; this is multiplied by the Stat Value to give a true indication of the worth of that statistic. This is then raised to the 1.7095 power (Log2/Log1.5) as shown below:

(StatValue[1]*StatMod[1])1.7095

This is repeated for every stat on the item and the totals are summed together, then raised to the 1/1.7095 power, to give the ItemValue:

The heart of the formula is to take each modified stat value to the 1.7095th power, sum up these terms and draw the 1.7095th root from the sum. This process makes single, high values of one stat more expensive than multiple, lower stats. Still it is a fairly simple mathematical model, but not so simple that it is just all the stats added together. Previously it was thought that the power was 1.5 or 1.6; calculations since have shown 1.7095 to be a more accurate model.

The stat modifiers or "StatMod" values are a "cost" associated with the stat, so an item of the same level can have more of a stat with a low StatMod, than with a high one. The same item could for example either have 5 mana regen/5 or 12 Spirit.

Stat

StatMod

Bonus armor

0.07 (1/14)

Armor Penetration

0.14 (1/7)

Attack Power vs (demons, beasts, undead) 2

0.33

Ranged Attack Power 2

0.40

Spell Healing 2

0.45 (5/11)

Attack Power

0.50

Spell Damage vs (demons, beasts, undead) 2

0.55

Blocking Value

0.65

Stamina (Burning Crusade and later items only)

0.67 (2/3)

Spell Damage (One school)

0.70 2

Spell Damage (All Spells)

0.86 (6/7)

Spell Penetration

0.80

Magic Resist (One school)

1.00

Primary Stat (STR, AGI, INT, SPI)

1.00

Stamina (pre-Burning Crusade Items only)

1.00

Combat Rating (Any)

1.00

Health per 5 sec

2.5

Mana per 5 sec

21

Magic Resist (All schools)

2.5

Damage Shield 2

3.15

Stealth Skill

2.00

+1 Stealth Level

7.00

1Mana regeneration cost 2.5 for every 1 mana/5 sec prior to patch 3.2. In patch 3.2, all items with mana regeneration had their amounts boosted by 25%, without changing their item level budgets. This means that mana regeneration now costs 2.0 for every 1 mana/5 sec.

2 These statistics are almost never found on Burning Crusade or Wrath gear.

Notes:

+Holy has value of 0.92 on some items (according to Hyzenthlei), while for example Green Lens will have the same +34-36 to any school including Holy

Magic Resist (All schools) includes items that specifically state "All Resistances", along with items that list each individual school.

An item that adds damage to two schools of magic may be charged anything between one school and all spells. This varies among a few items that do this which seemingly depends on usability of two schools for any classes.

These stat mods were obtained by evaluating several thousands of items. Some values (like resists or +spell damage) are pretty reliable since they occur on many items and in large values. Knowing the base that Blizzard uses, most others were rounded to a number that would appear to make sense.

Some item types have better or more stats than items that go in different slots. Helms for example will always give better benefits than bracers of the same item level. A high SlotMod in this table means that the item will have better stats than an item for a slot with a lower number and the same ilvl.

Many caster weapons sacrifice a portion of their Melee DPS to obtain spelldamage stats, for example the [Continuum Blade]. In this way, caster DPS and healer weapons gain spelldamage at an equivalent rate to melee weapons gaining melee DPS.
The amount of Damage/Healing/FAP gained is proportional to the amount of DPS sacrificed in the following way:

Spell Damage = Sacrificed DPS * 4

Healing = Sacrificed DPS * 7.5

Feral Attack Power = Sacrificed DPS * 18.37 - 12.4843

One Handed caster weapons universally have damage ranges between 41.0-42.0 DPS. This damage range is the basis for the sacrifice of DPS for both one and two handed weapons.

The amount of DPS Sacrificed simply Melee 1 Hand DPS - 41.5
In this way, a 2-handed caster staff and a one-handed dagger would both have the same spelldamage/healing.
The actual melee DPS of the caster weapon would then be:

Weapon Type

Uncommon

Superior

Epic

One Handed Caster

41-42

2 Handed Weapon Caster/Feral

0.3*Melee One Hander DPS + 41.5

To see how this works: A Superior iLevel 115 caster weapon such as the Continuum blade:

Armor value is inherent to the item and dependent upon its iLevel. Additional armor can be purchased with normal stat points: gear with additional armor will show the armor value in Green text. However, for most pieces the armor value is given without the use of any normal Item value.

The maximum armor for a particular iLevel piece is calculated using the formula below, and then multipied by the Armor SlotMod to calculate the armor for that particular gear slot. Blue/Superior armors have 1.1 times the armor value of a Green Item, and Epic items have 1.25 times the armor of a Blue item (1.375 times a green). Shields have a separate formula of their own and have different multipliers between gear qualities as shown below.

At one point the armor values of items seemed to decrease, but in a subsequent patch they returned to or exceeded their original values: [Dryad's Wrist Bindings] returned to normal but [Robes of Insight] gained 10 armor. The reasons for these changes are not yet known.

Socket research is still underway- it is not quite known how adding sockets affects an item's iLevel.

Currently there does not appear to be one set Statmod for sockets or any set way that they are added to items. Initial tests suggested that the Statmod may be around 10-11 but many items do not follow this basic pattern.

One theory proposed is that Sockets are created by removing stats from the item after it has been created, in order to make the item the correct iLevel for the 'expected' gems.

For example: Chestpiece of Tanking: Stats 50 Stamina, 40 Defense, 20 Strength. iLevel is calculated at 110 (blue item)
Then Stats are removed and sockets added in their place to take the place of those stats for the 'expected gems'.
12 Stamina is removed and replaced with a Blue Socket. - players are expected to socket this with Solid Star of Elune.
6 Stamina and 4 Defense is removed and replaced with a Yellow socket. - players are expected to socket this with Enduring Talasite.
6 Stamina and 4 Strength is removed and replaced with a Red socket. - players are expected to socket this with Sovereign Nightseye.
The item then becomes: 26 Stam 34 Defense 16 Srength, R B Y Sockets.

Note that defense bonuses were removed from the game.

The "expected gems" never add any new stats to the item, and always match socket colors.

Another theory is that the fundamental formula for calculating iLevel changes once sockets are added, but no progress has been made on this new formula.

It is also possible that empty sockets have no item level and different gems add an item level depending on their own stats.

Socket Bonuses are proportional in value to the amount of sockets. The socket bonus does not have any bearing on the ItemValue and is there to give players 'something for nothing' for choosing more diverse gems.
Socket Bonus for 1 socket has ItemValue of 2. (i.e. 3 Stamina, 2 Strength)
Socket Bonus for 2 sockets has Itemvalue of 3. (i.e. 3 Spellcrit, 1.2 Mp5)
Socket Bonus for 3 sockets has ItemValue of 4. (Ie, 4 Defense, 6 Stamina, 4.65 spelldamage)

The stat mods table contains the most frequently appearing stats. There are other stats which are sometimes unique or difficult to describe. All procs fall in this category, as do all Use:<do something> abilities. While these don't fit with an immediately obvious value, this system can be used to see what the blizzard item designers think they are worth and translate them into a stat-equivalent format.

This section concerns content that is out-of-date. Reason: In Patch 2.0?, armor formulas have changed.

Armor values on items follow a simple linear scaling pattern within certain limits. For example, mail armor scales linearly between certain ilvls, at which points the slope of the linear increase changes. One of these points is ilvl 45, above this point it scales more rapidly. Remember that an ilvl 45 item can be worn at lvl 40, and shamans and hunters get mail at 40. So they wanted mail to scale up fast for those classes, but without raising the amour values of pre 40 warriors too high (don't worry warriors, plate armor scales up even faster). Examples of armor scaling are shown below.

Green Plate Chest AC = (ilvl-44) * 8.9 + 428

Green Mail Chest AC = (ilvl-46) * 4.9 + 254

Green Leather Chest AC = (ilvl-40) * 2.2 + 110

Green Cloth Chest AC = (ilvl-40) * 1.2 + 53

Green Shield AC = (ilvl-44) * 28.3 + 1380

This only applies between a certain level boundary, in this case between X and 65, where X is found using the general formula of "(ilvl - X) * Y + Z", although they will most likely also apply post-level 65, as there are no big armor changes past that level.

The armor value of rare or epic pieces is also very easy to obtain using a simple multiplier. If you really want to go into detail, you will notice that there are plate chests with ilvls below 44. Due to their ilvl they should be equippable below lvl 40 (if any class could) and follow a different scaling equation (which is why jouster plate stuff has such pitiful armor values compared to many other starting plate item, their ilvls are all low).

For Items of the same armor type (cloth, leather, etc.) and the same ilvl

Rare Armor Value = Green Armor Value * 1.1

Epic Armor Value = Green Armor Value * 1.2

The exception to this is shields, which use a slightly different scaling

Of course there are items with much higher armor than others around that lvl. Those items are using the extra armor as an actual stat. Only this extra armor, above and beyond the predicted armor is considered in item weighting. So while the base armor level of an item is free, going higher will cost you other stats.

The item slot plays a role in armor as well:

Slot

Armor Multiplier

Fraction

Chest

1.00

16/16

Legs

0.875

14/16

Head

0.812

13/16

Shoulder

0.750

12/16

Feet

0.69

11/16

Hands

0.624

10/16

Waist

0.562

9/16

Wrist

0.438

7/16

Back (always Cloth)

0.480

*Notes
- Tier 4 plate armor seems to scale differently - the numbers crunched to 1325.28 rather than the 1510 that is actually on the piece. Perhaps a change is made to the scaling past iLvl 100-120?

This may include rewriting sections to ensure they are clear and concise, and wikifying.

-- In 2.0, this section may no longer be applicable.

Just like AC, you can also calculate weapon DPS. Before you continue however, make sure you read the parts about AC and DPS sacrificing, from here it is assumed you know what is written there.

The idea is far more simple than the AC, as there are no equivalent to armor types in DPS. This is the calculation for green onehanders:

Green One Hander DPS = ( ilvl - 45 ) * 0.6 + 26.6

But instead of having multiple formulas, you just have to multiply the DPS of a green onehander of the same level with a certain number, linked to what kind of new weapon you have, to give the DPS of that weapon:

Modifier

DPS Multiplier

Two Hand

1.305

Ranged (bow, gun etc.)

1.275

Wand

1.522

Superior

1.105

Epic

1.215

Besides these multipliers, raid items (some other items maybe as well) can sacrifice DPS for stats, in that case you simply have to subtract that from the expected DPS.

Note:

This seems to fit in the item range of level 45-65, before the green items have a different formula and after might scale differently. Also, these multipliers could be off, or each case could be a formula on their own, but it fits so well it seems unlikely.

The iLevel (Item Level) of an item often determines the level required to use that item. There are two separate formulas for this attribute. The first can be used on items acquired before Burning Crusade, the second on those after this expansion came out.

These are estimates based on the initial items datamined from the expansion. Though possible, these values are unlikely to change given their consistency with the rest of the formulas here. Blues seem to have different "levels" of blue with minLevel 80 being either iLevel 174 or 187. Heroic mode Blue drops are iLvl 200.

These are the general formulas. There are items, however, that do not follow these rules. Here is a (by no means complete) list of often occurring exceptions:

Quest items often have an iLevel of 1, or the level of the quest they belong to. In most cases, minLevel = iLevel in these cases.

Some quests give items whose minLevel is higher than the level needed to complete the quest. Because items obtained from quests in most cases don't have a minLevel, you can therefore have items with a higher iLevel than you can normally get.

Some items don't follow the formulas without apparent reason, especially in TBC. For example, [Terokk's Nightmace] has an iLevel of 115, but instead of the expected minLevel 70, it has a minLevel of 68.

The most exceptions are the items of epic quality, before TBC they tend to follow the rules for minLevel throughout level 1-59, but at level 60 and beyond the minLevel is capped. This is because of raiding instances. Items in these instances need to become more powerful in harder instances so people can become stronger even though they can't advance in level any more. Therefore, the iLevel of these items become higher, while players stay at level 60, so to be able to use these items, the minLevel is capped at level 60 for items before TBC, and at 70 for items in TBC.